Fluorescent lamps have been commonly known and widespread lighting devices as efficient alternatives for incandescent lightbulbs. However, with the advent of LED lamps (LED being the abbreviation for light-emitting diode), even more efficient and long-lived lighting means are available. Furthermore, in comparison to fluorescent lamps, materials of LED lamps are safer since, for example, no mercury is required. Therefore, there is a demand for replacing existing fluorescent lamps with LED lamps, preferably without having to change the entire luminaire or the lamp fixture.
Currently available fluorescent lamp fixtures normally comprise so-called electronic ballasts (also called electronic control gear, ECG) for regulating and limiting the current that is provided to the fluorescent lamp. The electronic ballast usually operates the lamp at high frequencies of up to 50 kHz. The frequency of the electronic ballasts is chosen such that the resonance frequency of the fluorescent gas is hit, thereby enabling active control of the current through the fluorescent lamp and resulting in an increased efficiency of the fluorescent lamp.
Some electronic ballasts have a residual voltage output after the electronic ballast has been turned off. This residual voltage output is due to residual energy stored in the electronic circuit of the electronic ballast. After turn-off, i.e. power down, this residual energy is released slowly, thereby causing residual voltage and/or current pulses at a frequency of less than 10 Hz. If a regular fluorescent lamp tube is connected to the electronic ballast, these residual pulses will not cause the fluorescent lamp to restart since the voltage is too small. However, in the case of an LED lamp, in particular a passive LED tube lamp, being connected to the electronic ballast, the residual voltage and/or current pulses are high enough to restart the LEDs in the LED lamp, thus causing flickering and/or flashing of the LED lamp. After the electronic circuit of the electronic ballast is de-energized, no more residual voltage and/or current pulses can be observed.
For connecting an LED lamp to an electronic ballast, LED lamps usually comprise a lamp driver that adjusts the voltage and/or current provided by the electronic ballast to the voltage and/or current requirements of the LEDs. However, currently available lamp drivers do not solve the problem of flickering and/or flashing during turn-off of the LED lamp by turning off the electronic ballast.